By powerlines do you mean different circuits from one breaker/fuse panel or separate circuits being served by two different power meters?
Powerline adapters work best if on the same circuit (i.e., common breaker or fuse). No power bars, surge protectors etc. permitted. Other loads may affect performance.
Powerline adapters may work across different circuits in the same location being served by the same breaker/fuse panel. Performance may be degraded depending on the wiring schematic, age, condition, other loads, etc. of and on those circuits.
However, powerline adapters are not intended for and won't work if one adapter is being served by one meter location and the other adapter is on another meter.
So if the house and granny...